Reversible free radical generation in the melanin granules of the eye by visible light.

Abstract By electron-spin resonance measurements, the melanin granules of the mammalian eye have been shown to generate free radicals when irradiated with visible light under approximately physiological conditions. The generation in the light and decay in the dark of the free radicals takes place over a period of seconds. The equilibrium concentration of free radicals in light or dark is dependent on the concentration of water, hydrogen ions, and dissolved oxygen in the surrounding solution. The anatomical proximity of the melanin granules to the rods and cones and their response to light suggests that the melanin granules may play an important role in the visual process.